Print hammer firing circuit

ABSTRACT

A circuit for firing print hammers of the type in which a plurality of hammers are provided in a magnetic core structure having a common yoke portion and a plurality of individual yoke portions. A common holding coil provides holding flux for holding the hammers in the normal or retracted position. An individual bucking coil associated with each hammer provides an impulse of bucking flux for overcoming the holding flux and causing the hammer to fire under spring tension, whereafter the holding flux restores the hammer to its retracted position. A proportional coil or winding, linked to the common portin of the magnet yoke, is connected so that the sum of the hammer firing currents in the bucking coils flows through the proportional coil or winding. This flux cancels out the effects of flux induced by the bucking flux in adjacent individual magnetic yokes, and thereby reduces hammer flight time variations.

United States Patent 11 1 1111 3,833,870 Wallace 1 1 Sept. 3, 1974 PRINTHAMMER FIRING CIRCUIT [57] ABSTRACT [75] Inventor: Leonard .1. Wallace,Vestal, NY. [73] Assignee: International Business Machines A circull forfinng prim hammers type in which Corporation Armonk, NY. a plurality ofhammers are prov1ded 1n a magnetlc core structure havmg a common yokeport1on and a Filedi 1973 plurality of individual yoke portions. Acommon hold- [21] APPL NOJ 406,722 ing coil provides holding flux forholding the hammers in the normal or retracted position. An individualbucking coil associated with each hammer provides an U.S. C, impulse ofbucking flux for vercoming the [5 Int. Clflux and causing the hammer tofire under pring ten. Field of Search 155-5, 1316- 4; sion, whereafterthe holding flux restores the hammer 101/93 335/263 to its retractedposition. A proportional coil or winding, linked to the common portin ofthe magnet yoke, References Cited is connected so that the sum of thehammer firing cur- UNITED STATES PATENTS rents in the bucking coilsflows through the propor- 3,285,165 11/1966 Richter 317 010. 4 {1011111coil of winding- This flux Cancels out the effects 3,423,641 1/1969Feldt 317 137 of flux induced by the bucking flux in adjacent indi-3,505,950 4/1970 Harper 101/93 C vidual magnetic yokes, and therebyreduces hammer 3,735,696 5/1973 Dayger et a1 101/93 C flight timevariations,

Primary Examiner-J. D. Miller Assistant Examinerl-larry E. Moose, Jr.Attorney, Agent, or Firm-Paul M. Brannen 6 Claims, 4 Drawing FiguresPmmiuw w 3.833.870

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PATENIEB E 3.833.870

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PROPORTIONAL FLUX PRINT HAMMER FIRING CIRCUIT FIELD OF THE INVENTIONDESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings,particularly FIGS. 1 and 2,

This invention relates generally to electromagnetic 5 there is shown aprint hammer assembly having a comapparatus, and particularly to animproved electromag netic print hammer firing circuit.

DESCRIPTION OF THE PRIOR ART Print hammer firing circuits of the typecomprising a common hold coil or winding on a common position of amagnetic yoke structure, and an individual bucking coil associated withthe individual yoke leg or branch provided for each hammer, are wellknown in the art, and various circuit arrangements have been utilized incontrolling print hammers of this type, as shown for example in U.S.Pat. No. 3,423,641.

SUMMARY OF THE INVENTION Generally stated, it is an object of thisinvention to provide an improved hammer firing circuit forelectromagnetic print hammers.

More particularly, it is an object of the present invention to providecompensating means on a print hammer assembly which will compensate forthe adverse effects normally encountered when a plurality of hammers arefired simultaneously.

Another object of the invention is to provide compensating means for thepurpose described above, which is simple and economical to provide.

In practicing the invention, a print hammer assembly in which there area plurality of individual hammers, each having associated therewith anindividual magnetic core portion, and those portions being connected toa common magnetic core structure, is provided with a compensating coilor winding linking the common portion of the core structure. Thiswinding is connected in series with the individual bucking coilsassociated with individual hammers and core portions, so that theinstantaneous sum of all the hammer firing currents flow through thecompensating winding in a direction such that the compensating flux aidsthe flux generated by the bucking coils and opposes the flux generatedby a common holding coil. By suitable selection of the number of turnson the windings, the compensating flux will counteract the effects ofsimultaneous firing of a plurality of hammers.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

DESCRIPTION OF THE DRAWINGS mon core portion of magnetic material whichis formed of two portions 3 and 5, the end portion of portion 3 beingdivided into a plurality of separate legs or sec tions 7, one for eachof the individual print hammers 9.

The magnetic structure is energized by flux generated by the currentthrough a holding coil or winding 11, the holding coil'and the commonportion of the yoke being common to all of the hammers in the unit. Theholding flux could also be generated by a permanent magnet suitablydisposed with respect to the common portion of the yoke. As statedpreviously, the magnetic circuit is subdivided into individual legs orsections 7 for each of the print hammers, and each of these legs orbranches is provided with an individual bucking coil 13, which whenenergized bucks out or neutralizes the effects of the flux from theholding coil or winding 11 so that the associated hammer is operated.Each of the hammer units 9 is provided with an armature element l5welded or otherwise affixed to the hammer structure 9 which bears at itslower end a type element 17 that is either engraved or otherwise formedas an integral portion of the element 9, or is a type slug which iswelded in place. Two flexural elements 19 and 21 serve to support thehammer and to provide the force to propel the hammer. The force andhence the flight time can be adjusted by changing the amount ofinterference between the fulcrum spring 23 and the flexural element 19.A screw 25 is provided to adjust the amount of tension.

Thus far, the arrangement shown and described is well known in the priorart. Normally, the armature 15 is in an attracted position because ofthe magnetic flux generated by the current flowing through winding 11.However, when it is desired to have the print hammer mechanism operate,current is passed through the bucking winding 13 for the particularhammer which is to be actuated, which thereby sets up an opposing fluxthat cancels or decreases the amount of holding flux provided to thearmature l5, whereupon it will be released and the hammer mechanism willbe impelled to cause the type face 17 to impact the document and ribbonagainst a suitable platen, not shown for the sake of simplifying thedrawings.

It has been found that variations in the current supplied to the buckingcoils can be mainly attributed to cross-coupling between adjacent coilsor adjacent hammers. Also variations in the hold coil current are mainlyattributed to back-induced voltages caused by the firing of the circuitsand energization of the bucking coil. The voltages and resultant currentcaused by such induction in the hold and bucking coils is proportionalto the number of hammers fired.

In accordance with the present invention, there is provided means forcompensating for the effects of a number of hammers being firedsimultaneously to thereby reduce the flight time variation caused by themagnetic coupling when a plurality of hammers are fired simultaneously.In accordance with the present invention, this means includes acompensating winding 27, mounted on the common portion or yoke of themagnetic core structure as shown in FIGS. 1 and 2.

FIG. 3 shows the manner in which the compensating winding 27 isconnected to produce the desired result. As shown in this figure, all ofthe windings are illustrated in relationship to the magnetic core 5. Theholding coil 11 is continuously energized as shown to produce theholding flux in the common portion and also in the individual branchesof core 5. The winding 27 is connected so that the current flowtherethrough is in the opposite sense to the flow of current throughholding winding 11, as indicated by the conventional dot symbology usedin denoting transformer winding relations. One side of the buckingwindings 13 is commonly connected to the energy source through thewinding of coil 27 as shown. Each of the windings 13 is adapted to beselectively energized by the closing of a suitable switch such as theswitches 31. Although these switches are shown as conventional manuallyoperated switches, this is for the sake of convenience and it will beunderstood that in the usual case, suitable electronic switches areemployed. It is apparent from the drawing that the amount of currentflowing through the winding 27 will depend upon how many of the switches31 are closed at any one time to thereby simultaneously energize aplurality of the bucking windings 13. Also it will be seen that thiscurrent flow in winding'27 will be in a sense such that the fluxgenerated thereby will oppose the flux generated by the hold winding 11.

The flux relationships are also seen from consideration of FIG. 4, whichis a diagrammatic illustration of the various flux paths in the hammerassembly. The holding flux produced by winding 11 is shown in FIG. 4 asa series of solid arrows traveling in a clockwise direction. The buckingflux set up by energization of the bucking coils is shown as a dash linewhich travels through the core in a counterclockwise direction, and inthe same direction, namely counterclockwise, there is shown a dot-dashline to indicate the proportional flux set up by the winding 27.

of the printer assembly at higher speeds of operation.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

I claim:

1. In an impact printer of the type wherein means including a pluralityof print hammers are activated by an electromagnetic assembly comprisinga magnetic core structure having a common core portion and individualcore portions associated with each hammer, holding flux generating meanslinking the common portion of said magnetic core structure forgenerating a hold flux in said core structure, bucking flux generatingmeans associated with and linking each individual core portion forgenerating bucking flux in said individual core portions to therebyactivate the associated print hammer, the combination with the foregoingof compensating flux generating means linking said common portion ofsaid core for generating flux in opposition to said holding flux andproportional to the instantaneous sum of said bucking flux.

2. The combination as claimed in claim 1, in which each of said fluxgenerating means comprises an electromagnet.

3. The combination as claimed in claim 1, in which said holding fluxgenerating means comprises a continuously energized electromagnet.

4. The combination as claimed in claim 1, in which said bucking fluxgenerating means comprises an individual electromagnet for each of saidindividual core portions.

5. The combination as claimed in claim 2 in which the electromagnetscomprising the bucking flux generating means are connected in paralleland then in series with the electromagnet generating the compensatingflux, so that all of the current in the bucking electromagnets flowsthrough the compensating flux electromagnet.

6. The combination as claimed in claim 5, inlwhich each of the buckingflux electromagnets is governed by an associated switch, whereby one ormore electromagnets can be energized at any given time.

1. In an impact printer of the type wherein means including a pluralityof print hammers are activated by an electromagnetic assembly comprisinga magnetic core structure having a common core portion and individualcore portions associated with each hammer, holding flux generating meanslinking the common portion of said magnetic core structure forgenerating a hold flux in said core structure, bucking flux generatingmeans associated with and linking each individual core portion forgenerating bucking flux in said individual core portions to therebyactivate the associated print hammer, the combination with the foregoingof compensating flux generating means linking said common portion ofsaid core for generating flux in opposition to said holding flux andproportional to the instantaneous sum of said bucking flux.
 2. Thecombination as claimed in claim 1, in which each of said flux generatingmeans comprises an electromagnet.
 3. The combination as claimed in claim1, in which said holding flux generating means comprises a continuouslyenergized electromagnet.
 4. The combination as claimed in claim 1, inwhich said bucking flux generating means comprises an individualelectromagnet for each of said individual core portions.
 5. Thecombination as claimed in claim 2 in which the electromagnets comprisingthe bucking flux generating means are connected in parallel and then inseries with the electromagnet generaTing the compensating flux, so thatall of the current in the bucking electromagnets flows through thecompensating flux electromagnet.
 6. The combination as claimed in claim5, in which each of the bucking flux electromagnets is governed by anassociated switch, whereby one or more electromagnets can be energizedat any given time.